Antibiotic class with potent in vivo activity targeting lipopolysaccharide synthesis in Gram-negative bacteria.

Here, we describe the identification of an antibiotic class acting via LpxH, a clinically unexploited target in lipopolysaccharide synthesis. The lipopolysaccharide synthesis pathway is essential in most Gram-negative bacteria and there is no analogous pathway in humans. Based on a series of phenotypic screens, we identified a hit targeting this pathway that had activity on efflux-defective strains of Escherichia coli. We recognized common structural elements between this hit and a previously published inhibitor, also with activity against efflux-deficient bacteria. With the help of X-ray structures, this information was used to design inhibitors with activity on efflux-proficient, wild-type strains. Optimization of properties such as solubility, metabolic stability and serum protein binding resulted in compounds having potent in vivo efficacy against bloodstream infections caused by the critical Gram-negative pathogens E. coli and Klebsiella pneumoniae. Other favorable properties of the series include a lack of pre-existing resistance in clinical isolates, and no loss of activity against strains expressing extended-spectrum-ß-lactamase, metallo-ß-lactamase, or carbapenemase-resistance genes. Further development of this class of antibiotics could make an important contribution to the ongoing struggle against antibiotic resistance.

Thieno[2,3-b]pyridines--a new class of multidrug resistance (MDR) modulators.

To identify new potent multidrug resistance modulators, we have synthesized a series of novel thieno[2,3-b]pyridines and furo[2,3-b]pyridines, and examined their structure-activity relationships. All synthesized compounds were tested to determine BCRP1, P-gp, and MRP1 inhibitor activity, and most potent MDR modulators were also screened for their toxicity, cytotoxicity and Ca(2+) channel antagonist activity. Among these compounds, thieno[2,3-b]pyridine (6r) was found to exhibit a potent P-gp inhibitory action with EC50 = 0.3 ± 0.2 µM, MRP1 inhibitory action with EC50 = 1.1 ± 0.1 µM and BCRP1 inhibitory action with EC50 = 0.2 ± 0.05 µM and may represent suitable candidate for further pharmacological studies.

Styrylpyridinium Derivatives for Fluorescent Cell Imaging.

A set of styrylpyridinium (SP) compounds was synthesised in order to study their spectroscopic and cell labelling properties. The compounds comprised different electron donating parts (julolidine, p-dimethylaminophenyl, p-methoxyphenyl, 3,4,5-trimethoxyphenyl), conjugated linkers (vinyl, divinyl), and an electron-withdrawing N-alkylpyridinium part. Geminal or bis-compounds incorporating two styrylpyridinium (bis-SP) moieties at the 1,3-trimethylene unit were synthesised. Compounds comprising a divinyl linker and powerful electron-donating julolidine donor parts possessed intensive fluorescence in the near-infrared region (maximum at ~760 nm). The compounds had rather high cytotoxicity towards the cancerous cell lines HT-1080 and MH-22A; at the same time, basal cytotoxicity towards the NIH3T3 fibroblast cell line ranged from toxic to harmful. SP compound 6e had IC50 values of 1.0 ± 0.03 µg/mL to the cell line HT-1080 and 0.4 µg/mL to MH-22A; however, the basal toxicity LD50 was 477 mg/kg (harmful). The compounds showed large Stokes' shifts, including 195 nm for 6a,b, 240 nm for 6e, and 325 and 352 nm for 6d and 6c, respectively. The highest photoluminescence quantum yield (PLQY) values were observed for 6a,b, which were 15.1 and 12.2%, respectively. The PLQY values for the SP derivatives 6d,e (those with a julolidinyl moiety) were 0.5 and 0.7%, respectively. Cell staining with compound 6e revealed a strong fluorescent signal localised in the cell cytoplasm, whereas the cell nuclei were not stained. SP compound 6e possessed self-assembling properties and formed liposomes with an average diameter of 118 nm. The obtained novel data on near-infrared fluorescent probes could be useful for the development of biocompatible dyes for biomedical applications.

Antifungal activity of styrylpyridinium compounds against Candida albicans.

We synthesized a set of 13 new and earlier described styrylpyridinium compounds (N-alkyl styrylpyridinium salts with bromide or tosylate anions) in order to evaluate antifungal activity against C. albicans cells, to assay the possible synergism with fluconazole, and to estimate cytotoxicity to mammalian cells. All compounds were synthesized according to a well-known two-step procedure involving alkylation of γ-picoline with appropriate alkyl bromide and further condensation with substituted benzaldehyde. Compounds with long N-alkyl chains (C18 H37 -C20 H41 ) had no antifungal activity against the cells of all tested C. albicans strains. Other styrylpyridinium compounds were able to inhibit yeast growth at the concentrations of 0.06-16 µg/ml. At fungicidal concentrations, the compound with the CN- group was least toxic to mammalian cells, showed the most effective synergism with fluconazole, and only slightly inhibited the respiration of C. albicans. The compound with the 4'-diethylamino group exhibited the strongest fungicidal properties and effectively blocked the respiration of C. albicans cells. However, toxicity to mammalian cells was also high. Summarizing, the results of our study indicate that styrylpyridinium compounds are promising candidates in the development of new antifungal drugs.